1. Field of the Invention
The present invention relates to an image forming apparatus that employs an electrophotographic recording method, such as a laser printer, a copying machine, or a facsimile. In particular, the present invention relates to an image forming apparatus that causes a cleaning member, e.g., an elastic cleaning blade, to come into contact with and remove a developer from a latent image bearing member, e.g., an electrophotographic photosensitive member. Further, the present invention relates to a control method for driving the image bearing member.
2. Description of the Related Art
An electrophotographic image forming apparatus transfers a developer image (i.e., a toner image) formed on a surface of an image bearing member to a transfer material, i.e., a recording medium. Examples of the image bearing member are a photosensitive member, i.e., a latent image bearing member, and an intermediate transfer member. A cleaning device then removes residual toner remaining on the image bearing member after the developer image has been transferred to the transfer material.
In general, a blade cleaning method is employed as the cleaning device. In such a method, a flexible (having rubber elasticity) cleaning blade, i.e., a cleaning member, is caused to come into contact with the image bearing member at a predetermined pressing state. The cleaning blade thus cleans the image bearing member by scraping and removing the toner remaining on the image bearing member after the image is transferred. Further, the cleaning blade is generally caused to come into contact with the image bearing member counter to a rotation direction of the image bearing member when forming an image.
The cleaning blade in the above-described image forming apparatus employing the blade cleaning method may become turned over by friction generated between the cleaning blade and the image bearing member. There are techniques for performing low friction processing on a surface of the image bearing member or the blade to prevent such a blade turn over. For example, Japanese Patent Application Laid-Open No. 2001-305770 discusses applying a lubricant on the surface of the image bearing member to decrease a friction coefficient, so that the blade turn over can be reduced.
On the other hand, when the above-described image forming apparatus employing the blade cleaning method continues printing using sheets that generate a large amount of paper dust, the paper dust may become stuck between the cleaning blade and the image bearing member (e.g., photosensitive drum, hereinafter referred to as drum). If the image forming apparatus continues to print while the paper dust continues to be stuck, the drum may become scratched and may generate image deterioration by forming vertical streaks in the image. The amount of the paper dust becoming stuck can be reduced by performing the above-described low friction processing on the surface of the image bearing member or the blade. Since a frictional force between the image bearing member and the blade becomes small by performing low friction processing on the image bearing member, the paper dust becomes less firmly stuck. Another method for reducing the stuck paper dust is to rotate the image bearing member in an opposite direction after printing to release the stuck paper dust. U.S. Pat. No. 6,539,189 discusses such a method of reducing the stuck paper dust.
However, when low friction processing is performed on the image bearing member or the cleaning blade in the above-described image forming apparatus employing the blade cleaning method, two different types of image deterioration may be generated. The type of the image deterioration which is generated depends on a usage state of the image bearing member or the blade. Such image deterioration will be described in detail below.
Much of the lubricant applied on the surface of the blade or the image bearing member in the cleaning device becomes separated along with the rotation of the image bearing member in an initial usage state of the blade or the image bearing member. The separated lubricant often becomes collected at a leading edge of the blade along with the rotation of the image bearing member. The leading edge of the blade on which the lubricant is collected is then pressed against the image bearing member by a predetermined amount of pressing force or greater. As a result, the lubricant becomes marked on the image bearing member, so that the image forming apparatus outputs a deteriorated image having the horizontal streak.
Further, the amount of paper dust stuck between the blade and the image bearing member increases after the initial usage state of the blade or the image bearing member, even when the lubricant is applied on the surface of the blade or the image bearing member. The paper dust thus scratches the drum, and image deterioration due to vertical streaks may be generated.